Each year almost 20,000 children are born to hepatitis B virus (HBV)-infected women in the US. To prevent mother-to-child transmission of HBV, newborns receive Hepatitis B Immune Globulin (HBIG) and HBV vaccine. This method of neonatal HBV prophylaxis that was developed 20 years ago provides protection from infection to approximately 95% of infants. In 5% of infants prophylaxis is unsuccessful which leads almost always to chronic HBV infection. The long-term consequences of chronic hepatitis B virus (HBV) infection with its increased lifetime morbidity and mortality are considerable. Recent studies have found that the most important determinant of neonatal HBV prophylaxis failure is high maternal viral load. With the availability of newer drugs that have been effective in lowering HBV viral load and have been used safely in pregnancy the potential of improving on current neonatal prophylaxis practices has become possible. This application is submitted to provide support for the development of a phase III randomized placebo controlled clinical trial of lamivudine in pregnant HBV-infected women and their children to improve the efficacy of neonatal HBV prophylaxis. The purpose of this study is to evaluate whether lamivudine administered during late pregnancy and in the newborn period together with HBIG and HBV vaccine will be more effective than HBIG and HBV vaccine alone in preventing HBV transmission. Specifically, funding is requested for a planning period to finalize the design, procedures and protocol of this multicenter clinical trail. Funding is also requested to develop a technological infrastructure for data intake/management and a standardized procedure for data entry and to finalize collaborative arrangements with other enrollment sites, community groups and private-practice physicians serving communities most at risk for chronic HBV infection. These elements will be essential to allow the successful completion of this proposed trial that has important public health policy implications in the U.S. and worldwide.